1. Field of the Invention:
The present invention relates to a catalytic composite for decomposing organic substances such as fats and oils, which can be attached to the inner wall of a heating cooker; the present invention also relates to a heating cooker having the catalytic composite for decomposing and removing grease or stains formed from fats and oils that is present in the cooker at comparatively low temperatures.
2. Decription of the Prior Art:
In general, the following two methods are available for the decomposition and removal of grease or stains which is formed and attached to the surface of the inner wall of a heating cooker when fish, meat, or the like is cooked in the heating cooker. In this specification, the heating cooker includes an apparatus with a heating means; for example, an oven, an electric range, etc.
The first method employs a cooker, the cooking chamber of which has an enamel coated inner wall. Grease or stains that adheres to the surface of the enamel coating is thermally decomposed by raising the temperature of the chamber so that the surface temperature of the enamel coating is about 450.degree. C. or more.
The second method employs a cooker having a porous film that contains oxidation catalysts the film being attached to the inner wall of the cooking chamber. Such a porous film is formed from a mixture obtained by dispersing an oxide of transition metals such as an oxides of Mn, Cu, Fe, Co, Ni, or the like, or an oxide of alkaline earth metals, in a binder such as a metal salt of inorganic acids (e.g., a metal salt of phosphoric acid or silicic acid), or enamel. Grease attached to the inner wall of the chamber can be decomposed by oxidation at comparatively low temperatures by the catalytic action of the metal oxide.
However, the foregoing conventional techniques have the following disadvantages.
An enamel coating is liable to crack due to a heat shock when the coating is heated to a temperatures of 500.degree. C. or more, resulting in a separation from the surface of the iron substrate (i.e., the wall substrate). Thus, the iron substrate corrodes and the cooker cannot be used. Furthermore, in the above-mentioned process, high temperatures are required, thus, a large capacity heater is needed. Therefore, a safety problem arises.
In the method of using the porous film, it is desired that the porous film has a high degree of porosity for the purpose of having an area large enough to perform an efficient contact between the grease or stains to be decomposed and the catalyst, and having an area large enough to allow oxygen to be diffused throughout the interior of the film. However, if the porosity of the film is increased, then the hardness of the film lowers; the film is apt to be injured, or the adhesiveness between the film and the inner wall of the cooking chamber is decreased. Furthermore, tar and ash formed by the decomposition of various materials permeates the porous film and settles in voids of the film, resulting in a gradual deterioration of the purifying performance of the film.
The present inventors prepared several kinds of porous films containing the above-mentioned catalyst, and tested the porous film by using salad oil to see the decomposition ability. It was found that it was necessary to heat the porous film at a temperature of at least 400.degree. C. for about two hours so as to decompose it completely. It was found that if the heating temperature was lower, the decomposition was incomplete, and decomposition resides progressively increased.